The present invention relates to a system for controlling a carburetor of an engine mounted on a vehicle having a supercharger.
In an engine provided with a carburetor having a float chamber, if air pressure in the venturi of the carburetor is during a positive pressure at supercharging, fuel can not be supplied from the carburetor to the venturi, because air pressure in the float chamber is at atmospheric pressure. Japanese utility model application laid open No. 50-20929 discloses a system intended to solve such a problem. According to the prior art, the supercharging pressure is applied to the float chamber, so that fuel in the float chamber is fed to the venturi by the pressure difference between the float chamber and the venturi. In the system, the float chamber is always communicated with the intake passage of the engine through a supercharging pressure-applying passage. Accordingly, the float chamber is subject to be heated by the heat transmitted from the supercharger through the intake air. In addition, the temperature of the intake air is raised in dependency on the compression of the air by the compressor of the supercharger and the heat of the hot air is transmitted to the float chamber through the body of the carburetor.
On the other hand, under light load conditions, the pressure in the float chamber decreases with a decrease of the supercharging pressure. Therefore, percolation of fuel in the float chamber occurs because of the high temperature of the chamber and the low pressure therein, which will cause extreme enrichment of the air-fuel mixture.